The travel plans for many thousands of people are already in ruins, with airport operator BAA warning that Heathrow faces more delays and cancellations until potentially beyond Christmas Day.

At Gatwick Airport, planes were grounded until 6am today as Britain continued to suffer from the big freeze.

There were also warnings of more long queues for Eurostar passengers at St Pancras station in London, after thousands were forced to wait for up to eight hours yesterday in bitterly cold weather.

Last night first-aiders from St John Ambulance were sent in as a precaution while people shivered in lines that stretched around the terminal building.

Drivers face widespread icy roads today, with temperatures expected to fall to -17C in the north of England overnight, and parts of the south dropping to -8C.

Transport Secretary Philip Hammond relaxed the rules on night flights yesterday in a bid to ease the passenger backlog at Heathrow.

The Government has agreed to relax night flights, allowing for arrivals until 1am until Christmas. And flights into London will be allowed to operate 24 hours a day.

But despite the moves, the airport was likely to operate at a reduced capacity until Friday, Mr Hammond said.

In a statement, BAA said: ‘Passengers should anticipate further delays and cancellations in the following days and potentially beyond Christmas Day.

It added that ‘significant cancellations’ would extend into at least tomorrow, telling passengers to keep away from terminals unless they knew for sure their flight was operating.

The airport’s second runway continued to be on shutdown today.

Many areas of the airfield ‘will not be usable until Wednesday morning at the earliest’, the operator said.

At Gatwick 150 staff were working to clear snow and de-ice the planes overnight in the hope of reopening later today.

The big freeze has not only affected those trying to leave the UK by air.

After yesterday’s half mile-long queues at St Pancras, Eurostar urged people to only come to the station if they had a confirmed booking for travel today.

‘Thank you for your patience,’ the operator added.

The UK’s roads and rail network has also been badly hit.

Giving a statement to the Commons yesterday, Mr Hammond said disruption was ‘inevitable’ given the severity of the weather conditions and that the transport system would “struggle to recover’ in the days leading up to Christmas with more poor weather expected.

The strategic road network and rail network have performed ‘broadly satisfactorily’, he said.

But he appeared to take a swipe at the reaction of BAA.

‘The experience at airports, and Heathrow in particular, has however been different,” the Transport Secretary said.r after Christmas. And by December 27, there should be significant thawing,’ he said.